Direction finding (DF) refers to the establishment of the direction from which a received signal was transmitted. The transmission could be by radio or other form of wireless communication. A single DF receiver site can establish a line of bearing, and by combining direction information from two or more suitably spaced DF receiver sites, a transmission site may be geographically located.
The antenna function of a DF system may be implemented with an array of antenna elements, that is, a multiple of antenna elements coupled to a common source. For example, a high-frequency (2 MHz to 30 MHz) DF system might use an array of loop antennas arranged in either a linear or circular arrangement.
In general, the usefulness of an antenna system is dependent upon dimensions of the antenna elements and their arrangement. Practical constraints, such as size, may make a given antenna system useful over only a limited band of frequencies.
For this reason, a DF system may use a two or more antenna subsystems, each subsystem operational over an associated frequency band. A challenge of this type of design is providing good signal separation between subsystems.